1. Field of the Invention
The present invention relates to tackers, staples, and power-hammers, and specifically to such power tools provided with a continuous hammer preventive mechanism which includes an idle hammering mechanism.
2. Discussion of Background and Material Information
Manual tackers and staples are well known. In a manual type of such a device, however, the hammering of a needle tack nail or staple requires manual labor, and the size of a needle to be hammered is somewhat limited by the physical capabilities of the laborer. Consequently, the amount of work which can be accomplished is limited accordingly.
In an attempt to improve conventional tools of this type, tools were developed which utilize air pressure to drive the hammer. Such air actuated tools require an electromagnetic solenoid utilizing a commercial source of power to run the motor. Such prior art efforts, however, suffer from the following disadvantages. In case of utilizing air pressure, a separate air-compressor is required, and in case of an electromagnetic solenoid, electromagnetic attraction occurs because the solenoid is integral with the tool the device becomes relatively heavy.
An electric tacker using a motor to the hammer is designed so that a percussion hammer is urged in a percussion direction by means of a spring, and the percussion hammer is moved in an urging direction of the spring by rotation of the motor. When the operating switch is turned ON, the percussion hammer held at the position of the top dead center is pushed down by the force of the spring and the hammer head secured to the hammer impacts the needle mounted on the magazine to hammer a material to be hammered.
A problem occurs, however, where a motor is used to power the tool, and the motor continues its rotation during the operation of the switch operating lever, and thereby causing a succeeding needle to be hammered on the already hammered needle unless the tacker is moved immediately after one needle has been hammered or the switch is turned off. Also, even if the user turns off the switch in a timely fashion, the motor or a driving cam is difficult to stop suddenly due to their inertia, and double-hammering of needles often results regardless of such efforts. In an attempt to overcome this problem, the invention disclosed in Japanese Patent Application Laid-Open No. 135182/1985 has been proposed. This patent application discloses the use of control means which comprises a cam switch driven by a switch cam, a main switch composed of a double switch and a braking resistor. In the electric control means, previously mentioned above, there are many parts which increase the cost of the tool, and it is difficult to adjust timing between both the switches. In addition, the needle hammered by the hammer head is not always completely hammered depending on the nature of the material to be hammered. In such instances, only the hammer head is pushed down while maintaining the succeeding needle so as not to come out until the incompletely hammered needle is hammered again. This is commonly referred to as "idle hammering".
Although, the electric tacker, as described above, is provided with a spring force adjusting mechanism for the spring for urging the percussion hammer in the percussion direction, the tacker is not equipped with an idle hammering mechanism. Thus, the tacker sometimes failed to sufficiently cope with the situation only being equipped with the spring force adjusting mechanism for the spring.
In addition, in all such tools, the number of needles mounted on the magazine is limited and the quantity of needles is reduced as hammering proceeds. A mechanism indicative of the remaining number of needles is not equipped in the conventional electric tacker. Accordingly, in normal operation, one does not become aware of the fact that needles are empty until no needle is hammered out.